/Engine/Plugins/Animation/RigLogic/Source/RigLogicLib/Public/dna/layers/GeometryWriter.h
The mesh storage will be implicitly resized (if needed) to provide storage for the number of meshes that is inferred from the specified index.
void setVertexPositions ( std::uint16_t meshIndex, const [Position](API\Plugins\RigLogicLib\dna\layers\Position) * positions, std::uint32_t count )